This jogged my memory of a CCP4 newsletter article many years ago covering kinematical versus dynamic scattering in protein crystals and offering a correction that could be used. I think it was Lindsay Sawyer and Igor Polikarpov in the late 90’s. I apologize if I have the authors wrong but I thought it was a commentary well ahead of its time and with modern sources and low noise detectors, I am wondering if anyone has revisited this? Protein crystals are remarkably high quality until you cryocool them. Serial methods combined with instrument capabilities may rate a revisit to the use of the kinematical approximation versus application of dynamical theories? Certainly the computational power is available.
Just my 2 cents for the day. Best, Eddie Edward Snell Ph.D. Director of the NSF BioXFEL Science and Technology Center President and CEO Hauptman-Woodward Medical Research Institute BioInnovations Chaired Professorship, University at Buffalo, SUNY 700 Ellicott Street, Buffalo, NY 14203-1102 hwi.buffalo.edu<http://hwi.buffalo.edu/> Phone: (716) 898 8631 Fax: (716) 898 8660 Skype: eddie.snell Email: [email protected]<mailto:[email protected]> Webpage: https://hwi.buffalo.edu/scientist-directory/snell/ [hwilogo] Heisenberg was probably here! From: CCP4 bulletin board <[email protected]> On Behalf Of James Holton Sent: Thursday, May 28, 2020 11:34 AM To: [email protected] Subject: Re: [ccp4bb] Strange Pseudosymmetry Effects Be careful with electron diffraction and apparent absence violations. It is possible these weak spots are simply due to multiple scattering. If so, you would see them relatively stronger with larger crystals,but much weaker relative to the strong reflections when the crystal is smaller. Do you? -James Holton MAD Scientist On 5/27/2020 6:49 PM, Jessica Bruhn wrote: Hello, I am wondering if pseudosymmetry can cause weak reflections that mimic the doubling of one unit cell axis' length. Has anyone seen something like this before? I am processing data from a small molecule sample collected with electron diffraction from multiple crystals. For the b axis, it is not clear if the length should be 10A or 20A. There are spots with the correct spacing for b=20A, but every other spot seems weaker than the spots along k if I choose b=10A (this extends beyond (0,k,0)). I am unable to phase the b=20 data. I have solved this structure in P1 with b=10 and found four molecules in the ASU and in P212121 with b=10 resulting in one molecule in the ASU. In P1, three of the four molecules adopt the same conformation, but the fourth molecule is in an alternate conformation that causes only ~1/2 of the molecule to be consistent with the first three. In P212121 I see density for part of this alternative conformation, but the full molecule in this alternate conformation cannot pack properly in P212121. Based on these results and some orthogonal data, I think I should refine the solution in P1 with b=10. Does it seem reasonable that pseudosymmetry is causing these weak reflections along k hinting at a doubling of the b axis? Thanks in advance! Best, Jessica -- Jessica Bruhn, Ph.D Principal Scientist NanoImaging Services, Inc. 4940 Carroll Canyon Road, Suite 115 San Diego, CA 92121 Phone #: (888) 675-8261 www.nanoimagingservices.com<http://www.nanoimagingservices.com> ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 ________________________________ To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
